Danielle a hurricane; TD 7 forming off coast of Africa

Hurricane Danielle has stopped intensifying and is now looking a bit ragged this morning, but remains a respectable Category 1 hurricane with 80 mph winds. The intensity of Danielle's heavy thunderstorms has waned in the past few hours, and the organization of the storm is less impressive. This is probably due do strong upper-level winds out of the west that are creating a moderate 10 - 20 knots of wind shear, and injecting some of the dry air from the Saharan Air Layer (SAL) that surrounds Danielle. Danielle is over warm 28°C water, but is far from any land areas.

Figure 1. Morning satellite image of Tropical Storm Danielle (left side of image) and the forming Tropical Depression Seven (right side of image.)

Forecast for DanielleA powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm. History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%. As far as intensity goes, it is looking unlikely that Danielle will attain major hurricane status (115+ mph winds.) There is enough dry air and wind shear affecting the storm today that it will take several days for the storm to recover its strength, making it less likely the storm can hit Category 3.

The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity. For example, none of the models foresaw the development of 96L until just 3 - 4 days ago.

Figure 2. Plot showing historically the percent chance of a tropical cyclone in a given location impacting the U.S. East Coast. For storms in Danielle's current position (orange hurricane symbol), about 20% of them go on to hit the U.S. East Coast. For storms in 96L's current location (red circle with a "?" in it), the odds are also 20%. Image credit: Bob Hart, Florida State University.

96L (soon to be Tropical Depression Seven)Satellite images suggests that a tropical wave (96L) that emerged off the coast of Africa yesterday morning has developed a closed circulation, low-level spiral bands, and an increasing amount of heavy thunderstorms. While this morning's ASCAT pass does not show a clear closed circulation, satellite estimates of 96L's strength support calling this a 30 mph tropical depression. It is likely that this storm will be designated Tropical Depression Seven later today. 96L is already bringing heavy rain and strong, gusty winds to the southern Cape Verde Islands. Winds were sustained at 26 mph at Mindelo in the northwest Cape Verde Islands this morning, and 24 mph at Praia, the station closest to the center of 96L. Both stations were reporting widespread dust, due to strong winds blowing Saharan dust from the coast of Africa. However, water vapor satellite images show that only a modest amount of dry air is accompanying this dust, and dry air is currently not a major detriment to 96L. Wind shear is about 10 - 20 knots, and sea surface temperatures are warm, 28°C.

Forecast for 96L/Tropical Depression SevenWind shear is predicted to remain low, 5 - 10 knots, for the next four days. SSTs will cool a bit to 27°C by Thursday, but this is still above the 26.5°C threshold for hurricane development. Dry air will probably be the main inhibiting factor for 96L. Most of the intensity forecast models bring 96L to hurricane strength by four days from now, and this is a reasonable forecast. 96L should become Tropical Storm Earl later today or on Wednesday, and will probably bring sustained winds of 40 mph to the southernmost Cape Verdes Islands tonight and Wednesday.

The long range fate of 96L remains unclear. The storm is being steering by the same ridge of high pressure steering Danielle, and will initially follow a track similar to Danielle. 96L may encounter the cold waters stirred up by Danielle at times this week, inhibiting development. As 96L approaches the central Atlantic five days from now, the storm will encounter the same mid-Atlantic trough that will be steering Danielle, and 96L should turn more to the northwest. It is unclear at this point whether this trough will be strong enough to fully recurve 96L out to sea, east of Bermuda. This will, in part, depend upon how strong Danielle gets. A stronger Danielle is likely to create more of a break in the ridge of high pressure steering 96L, encouraging the storm to turn north and recurve out to sea. A weaker Danielle will make 96L more likely to miss recurvature, and follow a track to the west or west-northwest towards the U.S. East Coast early next week. History suggests that a storm in 96L's current location has only a 20% chance of making landfall on the U.S. East Coast.

When will the Caribbean and Gulf of Mexico get active?The large scale atmospheric circulation over the Caribbean and Gulf of Mexico currently features relatively dry, stable, sinking air. This is due, in part, to the Madden-Julian oscillation (MJO). The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The latest MJO forecast from the GFS model calls for the wet phase of the MJO to move into the Caribbean during the first week of September. However, keep in mind that forecasts of MJO activity 1 - 2 weeks in advance are not very skillful. The GFS model forecast of MJO activity made two weeks ago did fairly well for the first week, but poorly for the second week of the forecast.

Tropical Storm Frank spares MexicoOver in the Eastern Pacific, Tropical Storm Frank has moved away the coast far enough from the Mexican coast to no longer pose a heavy rainfall threat, and all tropical storm warnings have been dropped.

"Hurricane Haven" airing again this afternoonTune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. I'll focus on Danielle, Earl, and Frank, and discuss the possibilities of a hyperactive Atlantic hurricane period coming during the first week of September.

Quoting MiamiHurricanes09:The lack of an anticyclone centered over the circulation of Danielle is allowing the deep-layer ridge over the southeastern U.S to shear Danielle with 10-20 knots of westerly/southwesterly shear. Water vapor also shows some dry air being ingested by Danielle in the western quadrant thus allowing for some thunderstorm activity to drop in that quadrant. The northwestern edge of the circulation also appears to be exposed on satellite imagery (which by the way is located near 17.4N 47.9W). I wouldn't be surprised that Danielle be downgraded to a tropical storm...for now.

Quoting keisa90:OK, enough is enough with the StormW bashing! Storm takes time out of his day (almost everyday) to put together a synopsis and then answers questions throughout the day. Sometimes the same question over and over again. I'm sure it gets very frustrating sometimes to have to constantly repeat yourself. He's not getting paid to do this, he does it out of his love for weather and he wants to help those of us who truly want to learn more about storms. Now, I don't know Storm personally, but I say keep up the good work! There are many who appreciate you in this community. Off my soapbox. I'll go back to lurking now...

Someone's bashing StormW? How uncouth! Sign me up for the Poof Brigade! And no Storm, you do NOT come across as a grumpy old man. Not at all.

Check this loop out. You can see the circulation moving towards the NW with ease. Now that you spotted the circulation, the center of it is near 17.3N/17.4N. What you're looking at 17.0N is the southern portion of the circulation, not the center of it.

Where are all these outstanding conditions that the forecasters were calling for the 2010 season because of La Nina??? King TUTT and ULL"s with their dry air and shear have sure kept the Atlantic basin in check. The huge upper level trough carved out in the W Atlantic has been there for a little over 2 months now rotating ULL's one after another. Models are hinting a pattern change in 10 days. Guess we will see if it pans out or not. The clock is ticking on this hyperactive season.

Quoting Levi32:You know what would really be a great learning experience.....set up a group of students, or whatever, independent of the NHC, to draw up a forecast for a tropical cyclone without looking at any model tracks (or the NHC's forecast). True the skill would be pretty bad by days 4 and 5, same as our's were before computer models came into existance, but talk about a great way to learn some real forecasting. None of this model consensus nonsense.

Now your bringing back some memories. I think any old goat that is still around would tell you that the models of today are very useful tools. They are just that though--tools.

No, I never delved into it.. Water is a modifier in meteorology...you warm the water, you warm the surrounding atmosphere, you cool the water, you cool the surrounding atmosphere. That's why temps are always cooler at the coast during summer, and warmer near the coast during winter. Would be something very interesting to look into.

Well the way I think about it, teleconnections are really just a measure of the current environment. Think about it, ENSO, PDO, NAO, their values are all determined by some environmental characteristic, whether it is pressure or water temperature. So when you see a change in global temperature, it only makes sense that it would be reflected into the values of the teleconnections.

Quoting tpawxguy:Under the header, "A fool and his money". I was talking to a buddy today at AccuWeather and he said they were informed Orange Juice futures skyrocked today. Why? Bloomberg business said it was because of the fear of a hurricane hitting Florida next week. I couldn't help thinking the Duke brothers were involved somehow!!

I thought this was a weather blog, it's turning into an I like StormW blog...LOLI don't post much to this blog simple due to the fact that so many others are posting the questions I would ask anyway and already getting the answers from the more knowledgeable such as StormW. The fact remain that there isn't a question that doesn't get answered on this blog unless it gets missed and sometimes you get a difference of opinions to these same questions; but it makes you think. I don't have the time I use to have to devote to trying to predict where a weather system in headed, thankfully, I don't have to do my own research as most of what I am looking for is already posted for me. I think I'm getting lazy. With that being said, I suggest people stick to posting/blogging about the weather and stop trying to pick fights (trolls) about something that someone posted that might be incorrect. What's next grammar and spelling classes? btw: I am a grumpy old man, if you really want to go there.Now back to the weather, so do you really think that 96L will head back to Africa?

Under the header, "A fool and his money". I was talking to a buddy today at AccuWeather and he said they were informed Orange Juice futures skyrocked today. Why? Bloomberg business said it was because of the fear of a hurricane hitting Florida next week. I couldn't help thinking the Duke brothers were involved somehow!!

Anyone else thing that Danielle isnt going to make CAT 3 status? I think she'll be lucky to hang on to just being a hurricane. Earl will be the strong of the two IMO. There is just flat out too much dry air enveloping this system

Quoting Levi32:You know what would really be a great learning experience.....set up a group of students, or whatever, independent of the NHC, to draw up a forecast for a tropical cyclone without looking at any model tracks (or the NHC's forecast). True the skill would be pretty bad by days 4 and 5, same as our's were before computer models came into existance, but talk about a great way to learn some real forecasting. None of this model consensus nonsense.

Levi,This is brilliant. The weather underworld should make this a contest. Make it $10 to enter. Winner gets half and Porthole gets the other half. For those of us that don't wish to partcipate, we can sponsor someone else like you!

The lack of an anticyclone centered over the circulation of Danielle is allowing the deep-layer ridge over the southeastern U.S to shear Danielle with 10-20 knots of westerly/southwesterly shear. Water vapor also shows some dry air being ingested by Danielle in the western quadrant thus allowing for some thunderstorm activity to drop in that quadrant. The northwestern edge of the circulation also appears to be exposed on satellite imagery (which by the way is located near 17.4N 47.9W). I wouldn't be surprised that Danielle be downgraded to a tropical storm...for now.